1. Technical Field
This invention relates to a power-assisted bicycle including an electric motor that adds electrical driving force to the manual driving force.
2. Background Art
Such a power-assisted bicycle carries a battery that supplies electricity to the electric motor for producing the additional electrical driving force. Since it is desired that the bicycle can travel as long a period of time as possible between charges of the battery, a power-assisted bicycle is now known which is capable of using energy generated while the bicycle is traveling for regeneration of the battery.
JP Patent Publication 8-140212A discloses a regeneration device for regenerating the battery including a control device for detecting the operation of the brake bars and controlling the regeneration device to regenerate the battery.
In the case of a power-assisted bicycle including a motor and a transmission mounted around the axle (hub-motor type), regeneration of the battery is realized simply by directly connecting the axle to the rotor of the motor (see e.g. JP Patent Publication 2003-166563A).
But such a hub-motor type bicycle has a problem in that the distance between the motor and the secondary battery is long and thus it is necessary to connect them thorough a long wire. Further, if the motor is mounted on the front axle, steering becomes difficult. Also, it is difficult to mount both the motor and the transmission on the rear axle.
Thus, a power-assisted bicycle with a regenerative function preferably includes a center motor unit comprising a manual drive unit including a crankshaft and its bearing, a power drive unit including a motor and a mechanism for supplying the motor power to the crankshaft, and a single housing in which both the manual drive unit and the power drive unit are mounted (see JP Patent Publication 10-250673A). Such a bicycle is easy to operate and simple in structure.
A center-motor type power-assisted bicycle with a regenerative function is disclosed e.g. in JP Patent Publication 2001-213383A.
This power-assisted bicycle includes a first one-way clutch disposed between the motor output shaft and the drive sprocket, a second one-way clutch disposed between the pedal crankshaft, to which manual force is applied, and the drive sprocket, and a directly coupling means for locking the first one-way clutch when the brakes are operated to regenerate the battery during braking. The rear hub is directly coupled to the rear sprocket so that reverse input torque from the wheel can be transmitted to the motor for regeneration.
JP Patent Publication 2004-268843A also discloses a similar power-assisted bicycle with a regenerative function.
This power-assisted bicycle includes a two-way clutch mounted in the center-motor unit and connected to the motor output shaft, and adapted to be selectively locked in either direction when the brakes are operated, thereby regenerating the battery during braking.
In particular, while the bicycle is being driven both by the manual force and the motor power, the two-way clutch is locked in the forward direction, thereby transmitting the motor output to the axle. When the brakes are applied, the two-way clutch is locked in the reverse rotational direction, so that reverse input torque (in the forward rotational direction) is transmitted to the motor for regeneration. In this arrangement, since it is necessary to transmit reverse input torque from the axle to the motor for regeneration, the rear hub is directly coupled to the rear sprocket.
As described above, power-assisted bicycles are roughly classified into the center-motor type, in which the motor is located near the crankshaft, and the hub motor type, in which the motor is mounted in the front hub or the rear hub.
The hub motor type has a problem in that besides a motor, a speed reducer has to be mounted in the rear hub too, so that it is difficult to use a speed reducer which is large enough to provide high speed reduction ratios, which in turn makes it impossible to produce large torque. Also, since heavy objects are mounted at locations apart from the center of gravity of the bicycle, steerability of the bicycle is not good. Further, since the distance between the motor and the battery is long, it is necessary to connect them thorough a long wire. Still further, since shock from the wheel is directly transmitted to the speed reducer and the motor, they tend to malfunction. Thus, an increasing number of today's power-assisted bicycles are of the center-motor type.
In the bicycles disclosed in JP Patent Publication 2001-213383A and JP Patent Publication 2004-268843A, which are center-motor type bicycles having a regenerative function, the rear hub and the rear sprocket are directly coupled together so that reverse input torque from the wheel can be transmitted to the motor shaft.
On the other hand, transmissions of ordinary bicycles are classified into the externally mounted type, which comprises a multi-stage sprocket assembly coaxially mounted on at least one of the crankshaft and the rear axle, and a derailer for moving the chain across the sprocket assembly to engage the chain with any selected one of the sprockets, and the internally mounted, which comprises gears mounted in the rear hub and used selectively to transmit torque. A one-way clutch is ordinarily mounted in such an internally mounted transmission so that reverse input from the wheel is not transmitted through the rear hub to the rear sprocket.
An externally mounted transmission is simple in structure and lightweight, but its sprockets and chain tend to quickly become worn and its chain can easily separate. The internally mounted transmission is dustproof and waterproof and is free of maintenance. Thus the internally mounted transmission is frequently used in a city bicycle. Most power-assisted bicycles of today are city bicycles and their transmissions are mostly internally mounted transmissions.
But the conventional internally mounted transmissions cannot transmit reverse input from the wheel to the rear sprocket through the rear hub, and thus cannot turn the center motor for regeneration.
One way to transmit reverse input would be to connect the axle to the crankshaft and the axle to the motor shaft through two separate power transmission means. But the two separate power transmission means would markedly lower the value of the bicycle from the viewpoint of layout and cost.